1. Field of the Invention
This invention relates to a method of and apparatus for cooling a molten glass parison in a blank mold of a forming machine of the individual section ("I.S.") type. More particularly, this invention relates to a method of and apparatus for cooling the finish portion of a molten glass parison while it is positioned in such a blank mold.
2. Description of the Prior Art
Hollow glass articles, such as bottles and jars, when molded by a forming machine of the I.S. type, are molded in two steps. In the first step, a preform of the finished container, namely an article with a closed end and an open end, which is usually called a blank or a parison, is molded by an annular mold that is made up of a pair of mating blank mold sections. Upon the completion of the blank molding step, the blank mold sections separate, and the blank or parison is transferred to another mold station, often called the blow mold station, where it is blown into its final shape by another annular mold that is made up of another mating pair of mold sections. At the conclusion of the blow mold process, the mating sections of the blow mold are separated, and the container is removed from the forming machine for further processing.
The glass gob that is formed into a parison in the blank mold of an I.S. machine is sufficiently hot to be capable of being shaped into a parison and, thus, possesses a high level of latent heat. Much of this heat must be removed before the container is removed from the blow mold of the forming machine, however, so that the finished container will be sufficiently rigid to undergo further processing without any further change in its shape. Thus, much heat must be removed from the container being formed, both during the blank molding step and the blow molding step, and unless the heat is removed at a rapid rate, the productivity of the forming machine is unduly limited.
The problem of heat removal from the molds of an I.S. forming machine at a suitable rate is especially important at the blank mold station because the surface area of the parison is quite small due to the small diameter of the parison, which limits the rate at which heat can be removed, and the amount of heat to be removed is quite high due to the larger wall thicknesses of the parison in comparison to the wall thicknesses of a finished container.
An approach to the cooling of parisons at a blank mold station of an I.S. machine is disclosed in U.S. Pat. No. 3,580,712 (Mumford), the disclosure of which is incorporated by reference herein. The process described in the '712 patent is occasionally referred to as the "41 Process."
A parison that is formed in a blank mold of an I.S. machine has a body portion and a "finish" portion. The finish portion is the portion of the parison that is immediately below the rim at the open end of the parison, and the finish portion is usually molded into a threaded or otherwise configured closure-receiving configuration by a mating pair of neck mold elements that are positioned adjacent to the blank mold elements at the blank mold station during the forming of the parison. The arrangement of the aforesaid '712 patent, which serves to cool the body portion of a parison by directing cooling air against the exterior of the blank mold sections, is not as effective in cooling the finish portion of the parison because the neck mold elements are not exposed to contact by cooling air as are the blank mold elements. Thus, in arrangements similar to those of the '712 patent, cooling of the finish portion occurs mainly by conduction of heat from the neck mold elements to the blank mold elements rather than by convection to a stream of cooling air. Neck mold cooling by such an arrangement is somewhat slower than the blank mold cooling that results therefrom, and, unless the removal of the parison from the blank mold station is somewhat delayed, this will lead to some imprecision in the dimensions of the finish portion of the parison due to temperature differences between the finish portion and the body portion of the parison. Problems relating to the cooling of the neck mold elements at a blank mold station of an I.S. glass forming machine are addressed in U.S. Pat. Nos. 5,516,352 (Bogert et al.), 5,358,542 (Johnson et al.) and 4,659,357 (Doud). However, the arrangements of these references are complex and require much additional structure for the implementation of the cooling processes described therein.